An electrophysiology data acquisition system is used in biological experiments to monitor and record electrical signals from a subject (e.g., a cell) under test. In such experiments, a researcher may use an experimental rig in which the subject is disposed. The researcher may also secure an electrode or test probe to the subject, for example, using a patch clamp technique, and then analyze the electrical signals detected by the electrode. The electrical signals from the subject may be low-level signals generated by a high-impedance signal source. As a result, such signals may be especially susceptible to electromagnetic interference (EMI) from radiated and conducted emissions of equipment connected to a mains power source. Such EMI may distort the signal of interest and appear as a “noise” or “hum” waveform added to such signal. Further, such noise may be periodic in accordance with the frequency of the electrical current generated by the mains power source. Such frequency is typically 50 hz or 60 hz and low harmonics thereof.
The researcher may use power line conditioners, Faraday cages, avoidance of “ground loops”, and the like to isolate the experimental rig from environmental noise sources. Nevertheless, even when great care is taken, EMI may still be introduced in the electrical signal transmitted from the electrode to a data acquisition system. Further, if such electrical signal is affected by EMI at a time in the life cycle of the subject of interest to the researcher, the efforts of the researcher to prepare and isolate the subject may be for naught. Such EMI may result in lost time troubleshooting the experimental apparatus or, worse, in missing the time-window in which live cells must be measured and an irrecoverable loss of the cells.
Typically, an analog electrical signal supplied by the electrode is converted into a stream of digital samples using an analog-to-digital converter. Adaptive noise cancellation techniques may be used to estimate noise components in the stream of digital samples, subtract the estimated noise components from the stream of digital samples, and provide the resulting stream of samples to the researcher.
In some experiments, a passive recording mode may be used in which the system passively records data. In some cases, the system waits for a trigger (for example, from the user) to initiate recording and thereafter passively records data. Other experiments use an episodic stimulation mode in which stimulation is provided to the subject. Such stimulation may include exposing the subject to a chemical or a drug from one or more micro-pipettes, delivering an electrical voltage, exposing the subject to a visible or invisible light source, generating a sound, and the like. The response of the subject reflected in the signal therefrom is simultaneously displayed and/or recorded. Such response is typically displayed in fixed length sweeps. Each sweep is non-overlapping, and an internal timer, a manual pulse or an external pulse may trigger the start of such sweep.
The electrode monitoring the subject may record the stimulation provided to the subject and/or the control signals used to trigger such stimulation. An adaptive noise cancellation unit may erroneously interpret such stimulation signal as noise in the signal from the electrode and attempt to eliminate such erroneous noise from subsequent signals, and thereby corrupt noise-corrected samples generated thereby. The effects of the erroneous noise on the noise-corrected samples may persist for a significant amount of time.